for: Fertility (soil)

Fertility is the natural capability of giving life. As a measure, "Fertility Rate" is the number of children born per couple, person or population. This is different from fecundity, which is defined as the potential for reproduction (influenced by gamete production, fertilisation and carrying a pregnancy to term). In the English language, the term was originally applied only to females, but increasingly is applied to males as well, as common understanding of reproductive mechanisms increases and the importance of the male role is better known. Infertility is a deficient fertility.

Human fertility depends on factors of nutrition, sexual behavior, culture, instinct, endocrinology, timing, economics, way of life, and emotions. Animal fertility is no less complex.

Agriculture

See also arable land, soil fertility, harvest, Neolithic revolution.

Fertility is also applied to farmlands and plants, where it implies a capacity to yield large crops of sound fruits, seeds or vegetables.

Demography

The fertility rate is a demographic measure of the number of children per woman. Although it has been until recently considered to be a fairly reliable indicator of population growth, it is no longer so in much of Asia. Due to selective abortion and other factors, the ratio of women relative to men in populations is declining. Therefore, the fertility rate as it has traditionally been defined is no longer an authoritative measure of population growth in China, India,Myanmar, and Korea.

Human fertility

Both women and men have hormonal cycles which determine both when a woman can achieve pregnancy and when a man is most virile. The female cycle is approximately twenty-eight days long, but the male cycle is variable. Men can ejaculate and produce sperm at any time of the month, but their sperm quality dips occasionally, which scientists guess is in relation to their internal cycle.

Furthermore, age also plays a role, especially for women.

Menstrual cycle

Main: Menstrual cycle Women are only fertile a few days during a menstrual cycle. That is usually 2 days before and 2 days after the ovulation date. This fertile window, varies between from woman to woman, just like the ovulation date often varies from cycle to cycle for the same woman. The ovule is usually fertilisable for up to 48 hours after it is released from the ovary. However, sperm can survive inside the uterus between 48 to 72 hours on average, with the maximum being 120 hours (5 days).

Female fertility

The average age of menarche in the United States is about 12.5 years. In postmenarchal girls, about 80% of the cycles were anovulatory in the first year after menarche, 50% in the third and 10% in the sixth year. Women's fertility peaks around the age of 19-24, and often declines after 30. With a rise in women postponing pregnancy,http://findarticles.com/p/articles/mi_m1077/is_1_62/ai_n16807720 "Late-in-life Pregnancy" this can create an infertility problem. Of women trying to get pregnant, without using fertility drugs or in vitro fertilization: